1. Field of the Invention
The present invention relates to digital subscriber line (xDSL) network systems permitting transmission of digital data signals over conventional telephone lines used for plain old telephone service (POTS), and in particular to a subscriber circuit in a telephone central office, connected to an interface unit at a subscriber location through a conventional telephone line.
2. Description of the Related Art
The existing public telephone network has been increasingly used to transmit digital data although it was originally designed for transmitting analog voice signals.
Digital Subscriber Line (xDSL) technology allows the telephone service and high-speed data transmission service over POTS lines. Especially, data transmission of Asymmetric DSL (ADSL) permits transmission of digital data over the conventional twisted wire pairs that are used for POTS, providing for an upstream channel at a maximum rate of 1 megabits per second (Mbps) and a downstream channel at a maximum rate of 9 Mbps.
The basic ADSL architecture has an ADSL interface unit at the telephone central office and an ADSL interface unit at the subscriber location. Each ADSL interface unit includes a POTS splitter or filter and ADSL modem.
In Japanese Patent Application Unexamined Publication No. 11-308352, an ADSL communication system has been disclosed, which is provided with a path switch at each of the central office and the subscriber location. When the telephone service is stopped, a controller deactivates the splitter and activates the path switch to connect the subscriber line directly to the ADSL mode. As a result, the frequency bandwidth assigned to the telephone service can be efficiently used.
However, the conventional architecture as described above is provided with the splitter between the subscriber circuit and the subscriber terminal. In general, a splitter has a filter composed of a coil and a capacitor to split multiplexed signals on the subscriber line into an analog POTS signal and a high-speed digital data signal. Accordingly, it is not possible to properly perform an accurate subscriber line test through such a splitter.
An object of the present invention is to provide a subscriber circuit allowing a reliable and proper subscriber line test.
According to the present invention, a subscriber circuit connected to subscriber equipment through a subscriber line, includes: a splitter for splitting a signal on the subscriber line into a lower-frequency band signal and a higher-frequency band signal; a feeder for feeding a current to the subscriber equipment through the subscriber line; a path selector for selecting one of a first path and a second path between the subscriber line and the feeder, wherein the first path has the splitter inserted therein and the second path has no splitter inserted therein; and a controller controlling path selection of the path selector depending on whether a subscriber line test instruction is received from a host.
The path selector normally selects the first path. When the subscriber line test instruction is received, the path selector selects the second path.
According to an aspect of the present invention, a subscriber circuit connected to subscriber equipment through a subscriber line, includes: a splitter for splitting a signal on the subscriber line into a lower-frequency band signal and a higher-frequency band signal; a feeder for feeding a current to the subscriber equipment through the subscriber line; a switch connected to the subscriber line, for selectively connecting and disconnecting the feeder to the subscriber line; a path selector connected between the switch and the feeder, for selecting one of a first path and a second path, wherein the first path has the splitter inserted therein and the second path directly connects the feeder and the switch; and a controller controlling the switch and the path selector depending on whether a subscriber line test instruction is received from a host.
The path selector may include: a first selector having a first common port and first and second selection ports, wherein the first common port is connected to the switch and the first selection port is connected to the splitter; and a second selector having a second common port and third and fourth selection ports, wherein the second common port is connected to the feeder, the third selection port is connected to the first selection port of the first selector through the splitter to form the first path, and the fourth selection port is connected directly to the second selection port of the first selector to form the second path.
According to another aspect of the present invention, a subscriber circuit connected to subscriber equipment through a subscriber line, includes: a splitter for splitting a signal on the subscriber line into a lower-frequency band signal and a higher-frequency band signal; a feeder for feeding a current to the subscriber equipment through the subscriber line; a selector connected to the subscriber line, for selecting one of a first path and a second path, wherein the first path has the splitter inserted therein and the second path directly connects the feeder and the subscriber line; a switch for selecting one of the first path and the second path synchronously with the selector, wherein the switch selectively connects and disconnects the feeder to the subscriber line; and a controller controlling the switch and the selector depending on whether a subscriber line test instruction is received from a host.
Preferably, the selector has a first common port and first and second selection ports, wherein the first common port is connected to the subscriber line and the first selection port is connected to the splitter. The switch has a second common port and third and fourth selection ports, wherein the second common port is connected to the feeder, the third selection port is connected to the first selection port of the first selector through the splitter to form the first path, and the fourth selection port is connected directly to the second selection port of the first selector to form the second path.
As described above, according to the present invention, the splitter is incorporated within the subscriber circuit in such a manner that the splitter can be isolated from a current feeding system. Accordingly, a reliable and proper subscriber line test can be achieved.